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New evidence of magmatic-fluid-related phyllic alteration: Implications for the genesis of porphyry Cu deposits

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Harris, AC and Golding, SD (2002) New evidence of magmatic-fluid-related phyllic alteration: Implications for the genesis of porphyry Cu deposits. Geology, 30 (4). pp. 335-338. ISSN 0091-7613

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Abstract

The phyllic alteration in a number of circum-Pacific porphyry Cu-Au deposits is related to high-temperature saline magmatic fluids. This contradicts the widely used genetic models wherein phyllic alteration formed as the result of mixing between magmatic and meteoric fluids. At the Endeavour 26 North porphyry deposit in eastern Australia, the transition from early potassic to the main-stage phyllic alteration is associated with fluids that with time decline in total salinity, NaCl/KCl, and temperature from ~600 to ~550 degrees C. Calculated and measured delta^18 O and delta D compositions of fluids (5.1-8.5 parts per thousand, -57 to -73 parts per thousand delta D) confirm a primary magmatic origin for both the early potassic and main- stage phyllic alteration. These results are consistent with other recent studies (e.g., El Salvador, Chile, Far Southeast, Philippines, and Panguna and Porgera, Papua New Guinea) and suggest that, rather than these results being unusual, a major revision of porphyry Cu genetic models is required.

Item Type: Article
Keywords: copper, gold, magmatic, ore-forming fluids, porphyry
Journal or Publication Title: Geology
Page Range: pp. 335-338
ISSN: 0091-7613
Identification Number - DOI: 10.1130/0091-7613(2002)030<0335:NEOMFR>2.0.CO;2
Additional Information: The definitive version is available at http://www.gsajournals.org/perlserv/?request=get-abstract&issn=0091-7613&volume=30&page=335 This article was included as Science Magazine's Editors Choice (Science 26 April 2002: Vol. 296. no. 5568, p. 621) Editors' Choice: Highlights of the recent literature Porphyry ore deposits consist of valuable ore minerals, usually copper or gold, disseminated in a matrix of both small and large crystals of other minerals, usually quartz or feldspar. These hydrothermal deposits represent the last remnants of magmatic fluid to crystallize from a larger igneous intrusion. The concentration of metals such as copper is thought to be enhanced by the circulation of groundwater that transports these metals from the host rock. Harris and Golding measured the hydrogen and oxygen isotopic concentrations of fluid inclusions and of quartz and sericite grains in a porphyry copper and gold deposit from the Goonumbla volcanic complex in Australia. The isotopic signatures indicate that the deposits formed from high-temperature, saline magmatic fluids and that no groundwater circulation was involved. Thus, as has been shown at some other porphyry deposits, the gold and copper metals are coming solely from the magma, and their formation temperature is higher than expected. This revised model for porphyry ore formation may help economic geologists recognize new deposits. -- Linda Rowans
Date Deposited: 14 Dec 2006
Last Modified: 18 Nov 2014 03:12
URI: http://eprints.utas.edu.au/id/eprint/504
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